Fuse



June 23, '1959 DOL ET 2,891,475

FUSE,

Filed Dec. 27, 1954 THERMOPLAST SHEATH IMPREGNATED TH FLAME SUPPRESSING MATERIAL.

TEXTILE COVERING FOR coma ZWIIIIIIIIIIIIIIIIII I4 v '6 PENTAERYTHRITOL CORE NVENTORS Jaw/v EDMUND L 4 ATTORNEYS United States Patent FUSE John Edmund Dolan, Kilwinning, Kenneth John Brimley, Stevenston, and Beter Blaekwood Dempster, Saltcoats, Scofland, assignor's to Imperial Chemical Industries Limited, London, England, a corporation ofGreat Britain" -1 Application December 27, 1954, Serial No. 477,944 Claims priority, application Great Britain Fel'n'uary 1,1954

3Claims. '(Cl. 102-27) This invention is concerned with a. new and improved detonating fuse which on being detonated in inflammable gas mixtures will not cause ignition thereof;

Textile ,detonating fuses of variouslrinds comprising a core ofpentaefythritoltetranitrate. and a, sheath of textile material are well known and have been used for a Variety of applications. 'It is also known to provide these fuses with an outer covering of a thermoplastic material such as polyvinyl chloride or polyethylene; It has, however,

not previously been consideredpossible to use detonating fuses in inflammable gas mixtures :because of the danger of ignition thereof by the flame from the'detonating explosive'forming the core.

Detonating explosive compositions used for blasting operations in gassy mines are of low power and have a low velocity of detonation, i.e., less than 3,000 metres per second and these have been made safer for such use by the provision of a flame suppressing sheathing material, in amount by weight of the order of 50 percent of that of the explosive, round the outside of the explosive cartridge. Thus, for example, such an explosive which unsheathed can be fired in amounts of about 4 oz. in inflammable methane/air mixtures can when sheathed be fired in amounts of about 20 oz. without causing ignition. The use of high power explosives of high velocity of detonation in inflammable gas atmospheres, however, is not made safe by sheathing with these flame suppressing materials.

Although it is stated for instance in British specification No. 428,187 that fuse cords having a non-inflammable cover of polyvinyl chloride or certain related materials are particularly serviceable in fire damp pits, fuses having a core of pentaerythritol tetranitrate and an outer covering of polyvinyl chloride cannot be fired in the presence of inflammable gas mixtures without causing ignition of these mixtures.

The object of the present invention is to provide a flexible waterproof detonating fuse having a core of pentaerythritol tetranitrate which can be fired in inflammable gas mixtures without causing ignition thereof while still retaining the high initiating power and the high velocity of detonation of said core.

Further objects and advantages of the invention will be in part obvious and in part pointed out hereinafter.

The novel features of the invention may be best made clear from the following description and accompanying drawings wherein a safety detonating fuse embodying the invention is illustrated fragmentarily in longitudinal section.

preferred'thattheflame suppressor is in admixture with" the thermoplastic binder in the maximum amount which 'A'ocor'ding to the present invention a textile detonating fuse comprises a core comprising pentaerythritol tetranitrate and a sheath of a flexible waterproof thermoplastic composition of extrudable consistency between 60 C.

.bon'ate, potassiumchloride, sodium sulphite, barium hy droxide, ammonium chloride, ammonium bicarbonate and sodium silicofluoride. Cryolite, sodium bicarbonate and sodium chloride are, however, preferred on'account of their effectiveness, low cost and: availability. It is also permits a composition to be obtained having the desired plasticity and extrudability between 60 and 200 C.

The thermoplastic binder may be either non-inflammable'for inflammable as long as the desired amount of flame'suppres'sorcan be incorporated to produce a com-.' position having the necessary plastic properties. "Suitable binders include, for example a polyvinyl chloride, a polyethylene, rubber, a synthetic rubber, balata, gutta percha and bitumen.

The flame suppressor and the thermoplastic binder may be mixed together by any convenient method, for example by mixing on hot rolls or in a heated dough mixer. With some thermoplastic binders it may be necessary or desirable to include other ingredients such as plasticisers and antioxidants.

The detonating fuse of the invention can be used to extinguish an ignited inflammable gas and also for dispersing flame-extinguishing media contained in the sheath of the flexible waterproof thermoplastic composition.

The invention is illustrated by Examples 1-9 in the following table.

A number of lengths of textile detonating fuse are made having a core of pentaerythritol tetranitrate. One length is standard Cordtex (registered trademark) fuse and the others diifer from this only in having instead of the normal outer thermoplastic covering a sheath of the thickness and composition shown in the table below. These various fuses are then fired freely suspended in a methaneair mixture containing 9 percent methane, in an iron cylindrical chamber 20 ft. long and 5 ft. in diameter, to determine the maximum length which does not cause ignition thereof. The weight of pentaerythritol tetranitrate per foot length is in all cases 3 g. and the weights of flame suppressor are of the order of 9 g. per foot length.

Composition A consists of 69.4 parts by weight soft balata, 16.3 parts by weight neoprene, 5.1 parts by weight montan wax and 9.2 parts of a neutral organic solid antioxidant produced by the condensation of an aliphatic a1- dehyde and an aromatic base.

Patented June 23, 1959 Thlck- Outer Example Composition of ness of Diameter Length Fired Ignition Sheath Sheath of Fuse (17.)

Standard Cordtex 0. 21 0.5. Yes. Cryolite/Balata 6:1 0.034 0. N do 0.046

do 0.054 4 Cryolite/Balata 8:1 0. 034 5 do 0. 049 6 Sodium Bicarbonate] 0. 049

Composltion A 4:1. 7 Sodium Biearbonate/ 0.053 0.

Composition A 6:1. 8 do 0. 053 0. 248 150 plus 10 side No.

branches 1 a foot long. 9 do 0. 058 0. 248 2 x 75 ft. strapped No;

together.

In all the above examples of textile detonating fuses including the Cordtex fuse the velocity of detonation textile detonating fuse'as' claimed in claim 1 wherein the thermoplastic binder is a compound selected is 6,700 metr%/sec. and the powder is 93% blasting from the group consisting of polyvinyl chloride, poly- :gelatine.

The lengths given for Examples 7 to 9 are the upper limits which are considered permissible to be fired in said chamber without damage to it.

What we claim is:

1. A textile detonating fuse including a core comprising pentaerythritol tetranitrate and a flexible waterproof sheath, the composition of said sheath consisting essentially of a finely divided flame suppressor and a thermoplastic binder, the amount of said flame suppressor being greater than the amount of said thermoplastic binder, said flame suppressor being a compound selected from the group consisting of cryolite, sodium bicarbonate, sodium chloride, fluorspar, potassium bicarbonate, potassium chloride, sodium sulphite, barium hydroxide, am-

ethylene, natural rubber, synthetic rubber, balata, gutta percha and bitumen.

References Cited in the tile of this patent OTHER REFERENCES Bebie: Manual of Explosives, Military Pyrotechnics and Chemical Warfare Agents, The MacMillan Co., New York (1943), p. 136. (Copy in Div. 70.)

Colver: High Explosives, Crosby Lockwood and Son, London (1918), pp. 650, 651. (Copy in Div. 70.) 

1. A TEXTILE DETONATING FUSE INCLUDING A CORE COMPRISING PENTAERYTHRITOL TETRANITRATE AND A FLEXIBLE WATERPROOF SHEATH, THE COMPOSITION OF SAID SHEATH CONSISTING ESSENTIALLY OF A FINELY DIVIDED FLAME SUPPRESSOR AND A THERMOPLASTIC BINDER, THE AMOUNT OF SAID FLAME SUPPRESSOR BEING GREATER THAN THE AMOUNT OF SIAD THERMOPLASTIC BINDER, SAID FLAME SUPPRESSOR BEING A COMPOUND SELECTED FROM THE GROUP CONSISTING OF CRYOLITE, SODIUM BICARBONATE, SODIUM CHLORIDE, FLUORSPAR, POTASSIUM BICARBONATE, POTASSIUM CHLORIDE, SODIUM SULPHITE, BARIUM HYDROXIDE, AMMONIUM CHLORIDE, AMMONIUM BICARBONATE, AND SODIUM SILICOFLUORIDE, AND SAID SHEATH COMPOSITION BEING EXTRUDABLE BETWEEN 60* AND 200* C. 